A gas turbine engine includes a compressor, a combustor and a turbine. Air is drawn into the compressor of the gas turbine engine. This air is compressed in the compressor and then is directed under pressure toward the combustor. Fuel also is directed into the combustor and is burned with the compressed air.
The combustion gases prouced in the combustor are directed at high speeds and under high pressure to the turbine. These gases impinge upon and rotate arrays of turbine blades, thereby performing work which operates the compressor and creates the thrust of the engine.
The compressed air approaching the combustor typically will have a temperature of 700.degree. F. to 1200.degree. F. On the other hand, the combustion gases produced in the combustor typically will be between 3500.degree. and 4000.degree. F.
There are significant performance advantages in maintaining the combustion gases at high temperatures. Conversely, there are certain performance penalties associated with the use of compressed air to perform cooling functions throughout the engine.
Despite the desirability of maintaining high operating temperatures and minimizing the amount of compressed air diverted to cooling functions, the wall of the combustor must be cooled to prevent structural damage. A small portion of this cooling is achieved by the relatively cool compressed air that travels adjacent the outer surface of the combustor prior to being mixed with the fuel. However, in most prior art engines, this external flow of compressed air can not achieve a significant amount of cooling of the combustor wall. More particularly, the velocity of the compressed air would have to be quite high to achieve any substantial external cooling of the combustor wall. If the size of the compressed air passage around the combustor liner was dimensioned to achieve higher velocities, it also would result in a substantial pressure drop along the length of that liner, thereby resulting in an inadequate pressure of the air flowing into the combustor near the end of that passage. Conversely, if the passage was dimensioned to have a minimum pressure drop, the velocity of the air would not be sufficient to achieve the required cooling.
In view of the above, most cooling of the combustor wall in the prior art engines has been achieved by directing a portion of the compressor discharge through the combustor wall in a way that will cool the wall. For example, annular arrays of small apertures were provided in the wall of prior art combustors to enable cooling to be carried out from the inner surface of the combustor. Specifically, the combustor wall would be provided with appropriate structures (e.g. splash rings) to create a thin film of cooling air adjacent the inner surface of the combustor. The effect of this thin film of cooling air would dissipate quickly. Consequently it was necessary to provide several successive arrays of cooling air apertures along the axial length of the combustor wall. The spacing between these cooling air apertures very depending upon the particular operating characteristics of the prior art engine. In most instances, these array of cooling air apertures would be spaced one to three inches from one another in an axial direction.
It has long been considered desirable to maximize the amount of combustor wall cooling that is carried out external to the actual combustion chamber. In many instances, this has been achieved by providing cooling air channels or grooves through the combustor wall. References which show this technology include: U.S. Pat. No. 4,292,810 which issued to Glenn on Oct. 6, 1981; U.S. Pat. No. 4,296,606 which issued to Reider on Oct. 27, 1981; U.S. Pat. No. 4,302,940 which issued to Meginnis on Dec. 1, 1981; and U.S. Pat. No. 4,315,406 which issued to Bhangu et al on Feb. 16, 1982. Briefly, these references all are directed to combustors having laminated walls with a plurality of circuitous paths extending therethrough. The various layers of the laminated wall each are provided with an array of grooves on one surface with a separate array of apertures extending through the layer and into the grooves. The layers are arranged such that the apertures and the grooves in one layer periodically communicate with the apertures and the grooves in an adjacent layer.
Different versions of the above described structures are shown in U.S. Pat. No. 4,292,810, which issued to Glenn on Oct. 6, 1981, U.S. Pat. No. 4,414,816 which issued to Craig et al on Nov. 15, 1983 and U.S. Pat. No. 4,480,436 which issued to Maclin on Nov. 6, 1984, all of which include spaced apart layers and internal baffles. The structures disclosed in these references would appear to rely more upon the convective film cooling inside the combustor than they would on conduction through the wall.
Most of the references cited above are believed to have many drawbacks. In particular, the structures include considerable mass and tend to be expensive to manufacture. Furthermore, the various prior art constructions are believed to yield somewhat uneven heat transfer characteristics across the combustor wall. Additionally, it is believed that in certain instances these prior art constructions will contribute to too great a pressure drop along the length of the passage through which the compressed air travels enroute to the combustor. This may result in an undesirable mixing pattern of compressed air and fuel within the combustor.
In view of the above described deficiencies of prior art combustor liners, it is an object of the subject invention to provide a combustor wall that easily and efficiently can be cooled by compressed air travelling through the combustor wall.
It is another object of the subject invention to provide a combustor wall that provides an efficient and desirable flow pattern of air through the combustor wall for cooling purposes.
It is an additional object of the subject invention to provide a combustor wall that can be manufactured easily and inexpensively.
It is a further object of the subject invention to provide a combustor wall that is lightweight but strong.
It is still another object of the subject invention to provide a combustor wall that can readily be subjected to quality control inspections at various stages during the manufacture of the combustor.
It is still an additional object of the subject invention to provide a combustor wall that achieves the desired velocity rates and pressure drops and proper mixing of air in the combustor.
Another object of the subject invention is to provide a combustor wall that can easily be provided with apertures through which air can be directed for proper mixing with the fuel.